1885.] NATURAL SCIENCES OF PHILADELPHIA. 351 



heavy plates, is either cup- or saucer-shaped, with basal regions 

 deeph' concave, somewhat funnel-shaped. In the dorsal cup the 

 pentamerous sj'mmetry is interrupted by the basals only ; at the 

 ventral side, however, it is greatly disturbed. Anus central, lo- 

 cated at the top of the neck-like prolongation, or at the end of 

 a tube. 



Basals four, small, unequal in size, one of them larger than the 

 rest; axial canal five-rayed; its radii directed interradially, there 

 being two of them in the larger plate. As a rule the basals are 

 not seen externally, being placed at the upper end of the concav- 

 ity, which also involves the greater part of the first radials, and 

 frequently other plates. 



Radials in three orders, the tertiary radials, however, imper- 

 fectly developed, and taking rather the form of brachials. Pri- 

 mary radials 3X5; the first one large, wider than the other two ; 

 the second quadrangular, wider than high; the third hexagonal, 

 its upper side truncate for the reception of an interaxillary plate. 

 Secondaiy radials 2 X 2 X 5, all pentangular, the lower series larger 

 than the upper, those of the same division connected by horizon- 

 tal suture. The upper secondary radial is axillaiy, and supports 

 the tertiary radials, which are composed of two short transverse 

 pieces supporting the arms. 



Dorsal interradials three to each interradius, throughout the 

 genus, in young as well as in adult specimens. The lower one is 

 the largest plate in the calyx, and always decagonal. The two 

 upper plates are connected by a vertical suture to their full 

 length, and both combined are smaller than the lower one. Their 

 upper ends form a narrow quadrangular projection, which extends 

 to the top of the tertiary radials, and supports upon its truncate 

 upper side the interradial partition walls. The interaxillary plates 

 of the dorsal side consist of a single piece in each ray, placed 

 between the secondary radials. In form and dimensions it resem- 

 bles most remarkably the two upper interradial plates, its upper 

 end projecting in a similar manner to the top of the tertiary 

 radials, and also supporting a partition. The peculiar projections 

 between the arm sockets give to the specimen a very marked 

 appearance, and when the ventral side is not preserved, form a 

 reliable guide for generic identification. 



The ventral side consists of four rings of plates. The lower 

 ring is composed of five elongate interradials, which rest upon 



